I don't see a problem with your sticking with texinfo 4 if it suits. Of course many people hate Texinfo and always will, but Emacs was the original GNU package. It would be sad in the extreme if you abandoned Texinfo as the source format for the documentation.
Incremental compilation: that would be nice. What comes to mind is to somehow dump the processed tree for an included file. Then subsequent runs can read the dump instead of redoing everything. There would be many complications, of course. Hopefully Patrice or Gavin have a better idea. k
